Allocating cache for use as a dedicated local storage

ABSTRACT

A method and apparatus dynamically allocates and deallocates a portion of a cache for use as a dedicated local storage. Cache lines may be dynamically allocated and deallocated for inclusion in the dedicated local storage. Cache entries that are included in the dedicated local storage may not be evicted or invalidated. Additionally, coherence is not maintained between the cache entries that are included in the dedicated local storage and the backing memory. A load instruction may be configured to allocate, e.g., lock, a portion of the data cache for inclusion in the dedicated local storage and load data into the dedicated local storage. A load instruction may be configured to read data from the dedicated local storage and to deallocate, e.g., unlock, a portion of the data cache that was included in the dedicated local storage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/079,520, filed Apr. 4, 2011. The aforementioned relatedpatent application is herein incorporated by reference in its entirety.

BACKGROUND

The field of the invention generally relates to caching data and, morespecifically to allocating cache for use as a dedicated local storage.

Conventional data caches are configured to store data that is frequentlyaccessed by a processor to reduce the latency needed to read and writethe data to a backing memory. Data caches also reduce the bandwidthconsumed between the processor and backing memory since data is onlyread from the backing memory and stored in the cache when a cache missoccurs. Similarly, writes to the backing memory may be reduced when thedata cache is used since data is copied from the cache to the backingmemory when the data is evicted from the data cache.

In order to allow a data cache to also serve as a dedicated localstorage, one conventional data cache may be configured in a mode thatconverts half of the data cache storage for use as a fixed sizededicated local storage. The half of the data cache includes onlycontiguous cache lines. Furthermore, the contiguous cache lines of thededicated local storage are accessed using addresses that are outside ofthe address range of the backing memory. The size of the dedicated localstorage is fixed and the cache lines that are configured to form thededicated local storage are also fixed.

SUMMARY

The present invention generally includes a system, article ofmanufacture and method for dynamically allocating a portion of a cachefor use as a dedicated local storage. Cache lines may be dynamicallyallocated (and deallocated) for inclusion in (and exclusion from) thededicated local storage. Cache entries that are included in thededicated local storage may not be evicted or invalidated. Additionally,coherence is not maintained between the cache entries that are includedin the dedicated local storage and the backing memory. A loadinstruction may be configured to allocate, e.g., lock, a portion of thedata cache for inclusion in the dedicated local storage and load datainto the dedicated local storage. A load instruction may be configuredto read data from the dedicated local storage and to deallocate, e.g.,unlock, a portion of the data cache that was included in the dedicatedlocal storage. A push context instruction may be used to allocate aportion of the data cache as a dedicated local storage for a thread andstore the current context for a thread. A pop context instruction may beused to load the current context for the thread and deallocate theportion of the data cache as the dedicated local storage for the thread.

According to one embodiment of the invention, a method, system andarticle of manufacture dynamically allocates a portion of a cache foruse as a dedicated local storage. A first instruction defining theportion of the cache is received and existing data stored in the portionof the cache is evicted. A setting indicating that entries in theportion of the cache should not be evicted or invalidated and thatcoherency should not be maintained between entries in the portion of thecache and a backing memory is updated.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

So that the manner in which the above recited aspects are attained andcan be understood in detail, a more particular description ofembodiments of the invention, briefly summarized above, may be had byreference to the appended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 depicts a block diagram of a system in which embodiments of thepresent invention may be implemented.

FIG. 2 depicts a block diagram of a cache in the CPU shown in FIG. 1,according to an embodiment of the present invention.

FIG. 3A is a flowchart illustrating a method for allocating a portion ofthe cache for dedicated storage, according to an embodiment of thepresent invention.

FIG. 3B is a flowchart illustrating a method for allocating a portion ofthe cache for dedicated storage using an instruction, according to anembodiment of the present invention.

FIG. 3C is a flowchart illustrating a method for deallocating a portionof the cache for dedicated storage, according to an embodiment of thepresent invention.

FIG. 3D is a flowchart illustrating a method for deallocating a portionof the cache for dedicated storage using an instruction, according to anembodiment of the present invention.

FIG. 4A is a flowchart illustrating a method for allocating a portion ofthe cache for performing a context switch, according to an embodiment ofthe invention.

FIG. 4B is a flowchart illustrating a method for deallocating a portionof the cache for performing a context switch, according to an embodimentof the invention.

DETAILED DESCRIPTION

The present invention generally includes a system, article ofmanufacture and method for dynamically allocating a portion of a cachefor use as a dedicated local storage. Cache lines may be dynamicallyallocated (and deallocated) for inclusion in (and exclusion from) thededicated local storage. Cache entries that are included in thededicated local storage may not be evicted or invalidated. Additionally,coherence is not maintained between the cache entries that are includedin the dedicated local storage and the backing memory. A loadinstruction may be configured to allocate, e.g., lock, a portion of thedata cache for inclusion in the dedicated local storage and load datainto the dedicated local storage. A load instruction may be configuredto read data from the dedicated local storage and to deallocate, e.g.,unlock, a portion of the data cache that was included in the dedicatedlocal storage. A push context instruction may be used to allocate aportion of the data cache as a dedicated local storage for a thread andstore the current context for a thread. A pop context instruction may beused to load the current context for the thread and deallocate theportion of the data cache as the dedicated local storage for the thread.

In the following, reference is made to embodiments of the invention.However, it should be understood that the invention is not limited tospecific described embodiments. Instead, any combination of thefollowing features and elements, whether related to differentembodiments or not, is contemplated to implement and practice theinvention. Furthermore, although embodiments of the invention mayachieve advantages over other possible solutions and/or over the priorart, whether or not a particular advantage is achieved by a givenembodiment is not limiting of the invention. Thus, the followingaspects, features, embodiments and advantages are merely illustrativeand are not considered elements or limitations of the appended claimsexcept where explicitly recited in a claim(s). Likewise, reference to“the invention” shall not be construed as a generalization of anyinventive subject matter disclosed herein and shall not be considered tobe an element or limitation of the appended claims except whereexplicitly recited in a claim(s).

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as a “circuit,” “module” or “system.”Furthermore, aspects of the present invention may take the form of acomputer program product embodied in one or more computer readablemedium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Embodiments of the invention may be provided to end users through acloud computing infrastructure. Cloud computing generally refers to theprovision of scalable computing resources as a service over a network.More formally, cloud computing may be defined as a computing capabilitythat provides an abstraction between the computing resource and itsunderlying technical architecture (e.g., servers, storage, networks),enabling convenient, on-demand network access to a shared pool ofconfigurable computing resources that can be rapidly provisioned andreleased with minimal management effort or service provider interaction.Thus, cloud computing allows a user to access virtual computingresources (e.g., storage, data, applications, and even completevirtualized computing systems) in “the cloud,” without regard for theunderlying physical systems (or locations of those systems) used toprovide the computing resources.

Typically, cloud computing resources are provided to a user on apay-per-use basis, where users are charged only for the computingresources actually used (e.g. an amount of storage space consumed by auser or a number of virtualized systems instantiated by the user). Auser can access any of the resources that reside in the cloud at anytime, and from anywhere across the Internet. In context of the presentinvention, a user may access applications or related data available inthe cloud. For example, an application may execute on a computing systemin the cloud and dynamically allocate and deallocate portions of a datacache for use as dedicated local storage.

Referring now to FIG. 1 that depicts a block diagram of a system 100 inwhich embodiments of the present invention may be implemented. Ingeneral, the networked system 100 includes a client (e.g., user's)computer (two such client computers 114A-B are shown; also separately(and collectively) referred to as computer(s) 114) and at least oneserver computer (four such computers 130A-D are shown; also separately(and collectively) referred to as computer(s) 130. Computers generallyare single devices with resources for computer processing, includingprocessors, memory and storage.

Computer 114A and computer 130A are representative of one particularembodiment of a client and server, respectively. The computer 114A andcomputer 130A are connected via a network 129. In general, the network129 may be a local area network (LAN) and/or a wide area network (WAN).In a particular embodiment, the network 129 is the Internet. Computers130 may be network servers, web servers, or any other computer that usesa network adapter (NA) 116, e.g., NA 116A-B to communicate withcomputers 114 and other computers 130 over network 129.

The computer 114A includes a Central Processing Unit (CPU) 102 connectedvia a bus 113 to a memory 108, storage 110, an input device 109, anoutput device 111, and a network interface device 112. The input device109 can be any device to give input to the computer 114A. For example, akeyboard, keypad, light pen, touch-screen, track-ball, or speechrecognition unit, audio/video player, and the like could be used. Theoutput device 111 can be any device to give output to the user, e.g.,any conventional display screen or set of speakers, along with theirrespective interface cards, i.e., video cards and sound cards (notshown). Although shown separately from the input device 109, the outputdevice 111 and input device 109 could be combined. For example, adisplay screen with an integrated touch-screen, a display with anintegrated keyboard, or a speech recognition unit combined with a textspeech converter could be used.

The network interface device 112 may be any entry/exit device configuredto allow network communications between the computer 114A and thecomputers 130 via the network 129. For example, the network interfacedevice 112 may be a network adapter or other network interface card(NIC).

Storage 110 is preferably a Direct Access Storage Device (DASD).Although it is shown as a single unit, it could be a combination offixed and/or removable storage devices, such as fixed disc drives,floppy disc drives, tape drives, removable memory cards, or opticalstorage. The memory 108 and storage 110 could be part of one virtualaddress space spanning multiple primary and secondary storage devices.

The computer 114A is generally under the control of an operating system104, which is shown in the memory 108. Illustrative operating systems,which may be used to advantage, include Linux® and Microsoft Windows®.Linux is a trademark of Linus Torvalds in the US, other countries, orboth.

The memory 108 is preferably a random access memory sufficiently largeto hold the necessary programming and data structures of clientapplications. While the memory 108 is shown as a single entity, itshould be understood that the memory 108 may in fact comprise aplurality of modules, and that the memory 108 may exist at multiplelevels, from high speed registers and caches to lower speed but largerDRAM chips.

Illustratively, the memory 108 includes an application 106 that, whenexecuted on CPU 102, provides support for exchanging information betweenthe various servers 130 and locating network addresses at one or more ofthe servers 130. In one embodiment, the application 106 is a browserthat includes a web-based Graphical User Interface (GUI), which allowsthe user to navigate and display web-pages located on the Internet.However, more generally the application may be a thin client applicationconfigured to transfer data (e.g., HTML, XML, etc.) between the computer114A and the computers 130 via, for example, HTTP.

The CPU 102 may be configured to execute multiple threads and mayinclude a data cache. One or more portions of the data cache may bedynamically allocated and deallocated for use as a dedicated localstorage. Portions of the data cache may be dynamically allocated anddeallocated as needed to store state information for a particularcontext of a thread. The memory 108 is configured to include a backingmemory 125 for the data cache. Data is copied from the backing memory125 into the data cache and maintained in the data cache until the datais evicted and copied back to the backing memory 125. Importantly, thededicated local storage is not necessarily coherent with the backingmemory 125. Entries in the data cache that are included as part of thededicated local storage may not be evicted or invalidated.

Like computer 114A, computer 130A may also include a memory 132, aninput device 129, an output device 121, and a storage 210, that aresimilar to memory 108, input device 109, output device 111, and storage110, respectively. The CPU 134 may also be configured to executemultiple threads and may include a data cache. One or more portions ofthe data cache may be dynamically allocated and deallocated for use as adedicated local storage and the memory 132 is configured to include abacking memory 165 for the data cache that performs a function similarto the backing memory 125 relative to a data cache in the CPU 102.

FIG. 2 depicts a block diagram of a data cache 200 in the CPU 102 or 134shown in FIG. 1, according to an embodiment of the present invention.The CPU 102 or 134 includes multithreaded execution unit(s) 220 thataccess the data cache 200 for load and store operations. The data cache200 includes a tag unit 210, entry control unit 205, and entries 215.Data is stored in the entries 215, where a cache line may include one ormore entries and has a respective address. The tag unit 210 translatesthe addresses received from the multithreaded execution unit(s) 220 intocache lines and determines whether a request is a hit or miss. Theentries 215 may be organized in one or more “ways”, where a way is thenumber of different banks in which data may be stored. In other words,when the cache is modeled as storage organized in multiple columns, eachcontaining multiple rows (cache lines), a way is a column. An 8-waycache provides 8 different locations in which data for a particularaddress may be stored.

Typically, caches allow for a way to be locked so that data stored inthe locked way cannot be evicted or invalidated. The entry control unit205 maintains a lock bit for each way to indicate whether or not the wayis locked. In addition to allowing the locking of a way, data cache 200also allows for locking of individual cache lines or a block defined bya range of addresses. The entry control unit 205 is configured toperform locking and unlocking of portions of the entries 215 bymaintaining a lock bit for each cache line in entries 215. The entrycontrol unit 205 is also configured to maintain a valid bit for eachcache line in entries 215 and to perform invalidation, validation,eviction, and maintain coherency between entries 215 and the backingmemory 165 or 125.

When a cache line is locked the entry control unit 205 sets the validbit and the lock bit in order to ensure that the data stored in theentry is not evicted. When a locked entry is unlocked, the entry controlunit 205 clears the lock bit and the unlocked entry is then availablefor eviction. When the locked entry is unlocked and evicted, the entrycontrol unit 20 copies the data from the cache line to the backingmemory 165 or 125 and clears the valid bit and the locked bit. The entrycontrol unit 206 may also be configured to maintain a super-lock bit foreach cache line in entries 215. The super-lock bit is set to indicatethat an entry should not be evicted or invalidated and also that thecoherence should not be maintained between the entry and the backingmemory 165 or 125. In particular, when the entry is unlocked andevicted, the entry control unit clears the super-lock bit and the validbit, but does not copy the data from the cache line to the backingmemory 165 or 125.

Because the super-lock function is used to allocate a portion of thedata cache 200 for dedicated local storage, coherence is not maintainedbetween the entries within the portion of the data cache 200 and thebacking memory 165 or 125. In some cases the data stored in the portionof the data cache 200 is not also stored in the backing memory 165 or125. Instead, the data is generated by the multithreaded executionunit(s) 220, stored in the portion of the data cache 200 and loaded fromthe portion of the data cache 200. The super-lock features allowsportions of the data cache 200 to be quickly and dynamically allocatedfor use as dedicated local storage without consuming bandwidth betweenthe CPU 102 or 134 and the memory 108 or 132, respectively.

In one embodiment, a separate super-lock bit is not maintained by theentry control unit 205. Instead, the super-lock function is encodedusing the lock and valid bits. When a cache line is super-locked thelock bit is set and the valid bit is cleared. When a cache line isunsuper-locked the lock bit is cleared and the valid bit remainscleared. The data is not copied to the backing memory 165 or 125 sincecoherency is not maintained between super-locked entries and the backingmemory 165 or 125.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof code, which comprises one or more executable instructions forimplementing the specified logical function(s). It should also be notedthat, in some alternative implementations, the functions noted in theblock may occur out of the order noted in the figures. For example, twoblocks shown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions. Reference will bemade to elements introduced above and described with respect to FIGS. 1and 2.

FIG. 3A is a flowchart 300 illustrating a method for allocating aportion of the data cache 200 for dedicated storage, according to anembodiment of the present invention. At step 305, a definition of aportion of the data cache 200 to allocate as a dedicated local storageis received. The definition may specify one or more cache lines, ways,or a block corresponding to a range of addresses as the portion of thedata cache 200 to allocate. At step 310, the entry control unit 205determines if entries are available in entries 215 to allocate to thededicated local storage. If, at step 310, the entry control unit 205determines that entries are available for allocation, then the entrycontrol unit 205 proceeds directly to step 320. At step 320, the entrycontrol unit 205 indicates that entries in the portion of the data cache200 that are allocated for use as the dedicated local storage aresuper-locked by updating a setting associated with the portion of theentries 215 in the data cache 200. The updating may set the super-lockbit(s) for the portion of the entries 215 or the updating may set thelock bit(s) and clear the valid bit(s) for the portion of the entries215. Note that one or more additional portions of the data cache 200 maybe allocated to generate different dedicated local storages within thedata cache 200.

If, at step 310, the entry control unit 205 determines that entries arenot available for allocation, then at step 315 the entry control unit205 evicts existing data from a portion of entries 215. The entrycontrol unit 205 copies the existing data to the backing memory 125 or165 and clears the invalid bit(s) for the portion of the entries 215before proceeding to step 320.

FIG. 3B is a flowchart 325 illustrating a method for allocating aportion of the data cache 200 for dedicated storage using aninstruction, according to an embodiment of the present invention. Atstep 326, a store instruction that defines the portion of the data cache200 to allocate as a dedicated local storage is received. Theinstruction includes data or a pointer to data to be stored in theportion of the data cache 200 and may specify one or more cache lines,ways, or a block corresponding to a range of addresses to define theportion of the data cache 200. Steps 330, 340, and 335 are performed inthe same manner as steps 310, 320, and 315 of FIG. 3A. At step 345, theentry control unit 205 stores the data specified by the storeinstruction in the portion of the data cache 200 that is allocated foruse as the dedicated local storage.

FIG. 3C is a flowchart 350 illustrating a method for deallocating aportion of the data cache 200 for dedicated storage, according to anembodiment of the present invention. At step 355, a definition of aportion of the data cache 200 to deallocate as a dedicated local storageis received. The definition may specify one of more cache lines, ways,or a block corresponding to a range of addresses as the portion of thedata cache 200 to deallocate. At step 360, the entry control unit 205indicates that entries in the portion of the data cache 200 that aredeallocated for use as the dedicated local storage are unsuper-locked byupdating the setting associated with the portion of the entries 215 inthe data cache 200. The updating may clear the super-lock bit(s) for theportion of the entries 215 or the updating may clear the lock bit(s)(the valid bit(s) would already be cleared) for the portion of theentries 215. Note that it is possible to deallocate only a sub-portionof the entries 215 within a portion of entries in the data cache 200that were allocated as a particular dedicated local storage. In otherwords, all of the entries within an allocated portion of the data cache200 do not need to be deallocated at the same time.

FIG. 3D is a flowchart 365 illustrating a method for deallocating aportion of the data cache 200 for dedicated storage using aninstruction, according to an embodiment of the present invention. Atstep 370, a load and destroy instruction that defines a portion of thedata cache 200 to read and deallocate as a dedicated local storage isreceived. The instruction may specify one or more cache lines, ways, ora block corresponding to a range of addresses to define the portion ofthe data cache 200. At step 375, the entry control unit 205 reads thedata specified by the load and destroy instruction from entriesspecified by the load and destroy instruction that are in the portion ofthe data cache 200 allocated for use as the dedicated local storage.Step 380 is performed in the same manner as step 360 of FIG. 3C.

When one or more of the multithreaded execution unit(s) 220 performs acontext switch, the current context is stored and a new context isloaded into the execution unit. After processing of the new context iscompleted, the stored context is loaded into the execution unit tocontinue being processed. A push context instruction may be used toallocate a portion of the data cache as a dedicated local storage for athread and store the current context for a thread. A pop contextinstruction may be used to load the stored (current) context for thethread and deallocate the portion of the data cache as the dedicatedlocal storage for the thread. In a conventional system, a dedicatedstack storage may be used to push and pop thread context data.Alternatively, the thread context data may be stored to memory 108 or132, introducing additional latency and requiring consumption ofbandwidth between the CPU 102 or 134 and memory 108 and 132,respectively.

FIG. 4A is a flowchart 400 illustrating a method for allocating aportion of the data cache 200 for performing a context switch, accordingto an embodiment of the invention. At step 405, a push contextinstruction is received by the data cache 200. The push contextinstruction may define the portion of the data cache 200 to allocate foruse as a dedicated local storage for storing thread context state or theentry control unit 205 may determine the number of cache entries neededto store the thread context state based on information provided with thepush context instruction. The instruction may include or indicate thelocation of the current thread context data to be stored in the portionof the data cache 200. Steps 410, 420, and 415 are performed in the samemanner as steps 310, 320, and 315 of FIG. 3A. At step 425, the entrycontrol unit 205 stores the data specified by the push contextinstruction in the portion of the data cache 200 that is allocated(superlocked) for use as the dedicated local storage for the threadcontext state.

FIG. 4B is a flowchart 450 illustrating a method for deallocating aportion of the data cache 200 for performing a context switch, accordingto an embodiment of the invention. At step 455, a pop contextinstruction is received by the data cache 200. The pop contextinstruction may define the portion of the data cache 200 to deallocatefor use as a dedicated local storage for storing the thread contextstate or the entry control unit 205 may determine the portion of thedata cache 200 to deallocate based on information provided with the popcontext instruction. At step 460, the entry control unit 205 reads thepushed thread context state specified by the pop context instructionfrom entries that are in the portion of the data cache 200 allocated foruse as the dedicated local storage for storing the thread context state.At step 465, the entry control unit 205 indicates that entries in theportion of the data cache 200 that are deallocated for use as thededicated local storage to store the thread context state aredeallocated (unsuper-locked) by updating the setting associated with theportion of the entries 215 in the data cache 200.

The present invention generally includes a system, article ofmanufacture and method for dynamically allocating a portion of a cachefor use as a dedicated local storage. Individual cache lines may bedynamically allocated and deallocated for inclusion in the dedicatedlocal storage. Alternatively, cache ways or a block specifying anaddress range may be dynamically allocated and deallocated to define thededicated local storage. Cache entries that are included in thededicated local storage may not be evicted or invalidated. Coherence isnot maintained between the cache entries included in the dedicated localstorage and the backing memory. A store instruction may be configured toallocate, e.g., lock, a portion of the data cache for inclusion in thededicated local storage and store data into the dedicated local storage.A load and destroy instruction may be configured to read data from thededicated local storage and to deallocate, e.g., unsuper-lock, a portionof the data cache that was included in the dedicated local storage. Apush context instruction may be used to allocate a portion of the datacache as a dedicated local storage for a thread and store the currentcontext for a thread. A pop context instruction may be used to load thecurrent context for the thread and deallocate the portion of the datacache as the dedicated local storage for the thread. The super-lockfeatures allows portions of the data cache to be quickly and dynamicallyallocated for use as dedicated local storage without consuming bandwidthbetween the CPU and the backing memory.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A method of dynamically allocating a portion of acache for use as a dedicated local storage, comprising: receiving afirst instruction defining the portion of the cache; evicting existingdata stored in the portion of the cache; updating a setting indicatingthat entries in the portion of the cache should not be evicted orinvalidated and that coherency should not be maintained between entriesin the portion of the cache and a backing memory.
 2. The method of claim1, further comprising: receiving a second instruction; and updating thesetting to free the portion of the cache for storing data in the entriesin the portion and maintaining coherency between the entries and thebacking memory.
 3. The method of claim 2, wherein the second instructionis a load and destroy function and further comprising reading theentries in the portion of the cache before updating the setting to freethe portion of the cache.
 4. The method of claim 1, wherein the firstinstruction is a push context instruction and further comprising storingstate for a first thread in the entries in the portion of the cache. 5.The method of claim 4, further comprising: receiving a secondinstruction that is a pop context instruction; reading the state for thefirst thread from the entries in the portion of the cache; and updatingthe setting to free the portion of the cache for storing data in theentries in the portion and maintaining coherency between the entries andthe backing memory.
 6. The method of claim 1, further comprising:storing data to an entry in the portion of the cache by a first thread;and reading the data from the entry in the portion of the cache by asecond thread.
 7. The method of claim 1, wherein the first instructionis a load instruction and further comprising: storing data to an entryin the portion of the cache by a first thread; and reading the data fromthe entry in the portion of the cache by a second thread receiving asecond instruction.
 8. The method of claim 1, wherein the firstinstruction specifies an address range defining the portion of thecache.
 9. The method of claim 1, wherein the cache includes multipleways and the first instruction specifies at least one of the waysdefining the portion of the cache.
 10. The method of claim 1, whereinthe first instruction specifies a cache line defining the portion of thecache.
 11. The method of claim 1, wherein the setting includes a lockbit associated with a cache line and a valid bit associated with thesame cache line.